1. Field of the Invention
The present invention relates to hemodialysis apparatus, and more particularly to a system for minimizing the effects of water pressure transients on the accuracy and consistency of patient dialysis.
2. Description of the Prior Art
Hemodialysis machines used to extract waste from human blood of patients having kidney failures or disorders utilize a dialyzer in which the blood flows through one chamber and a dialysate solution flows through another chamber separated from the first chamber by a membrane. The dialysate picks up metabolic waste products and ultrafiltrate from the blood passing through the dialyzer. In many such machines, incoming water is first treated externally to the machine to remove impurities, and thereafter pressure controlled, filtered, heated, and applied to a proportioning pump which is also connected to a supply of concentrated dialysis solution. The proportioning pump produces a carefully controlled dialysate solution from the water and concentrate. For example, a 34 parts water and 1 part dialysate concentrate is typical. The dialysate may be applied to a flow controller or other means which controls the rate of flow of the dialysate through the dialyzer.
To maintain the exact flow, pressure, and concentration of the dialysate through the system for consistent dialysis performance, it is necessary that the water flow and transients be minimized. Otherwise, such transients in the incoming water pressure will occur and will degrade the accuracy of the ultrafiltration control system. Although systems utilize pressure regulators to maintain the pressure, these regulators suffer from normal hysteresis and inertial effects which permit a drop or rise in pressure before correction can occur. Therefore, there is a need for a system which will maintain a constant pressure of water to the dialysate proportioning pump and flow controller when the input pressure and flow varies or experiences transients.